Semiconductors: A General Introduction Chapter 1. Semiconductors: A General Introduction Sung June Kim kimsj@snu.ac.kr http://nanobio.snu.ac.kr

Subject What is a semiconductor? Why does lattice have a periodic arrangement? What lattice structure does Si have? How does semiconductor grow?

Contents General Material Properties Crystal Structure Crystal Growth

Semiconductor Materials II III IV V VI B C Al Si P S Zn Ga Ge As Se Cd In Sb Te (b) Elemental IV compounds Binary III-V compounds Binary II-VI compounds Si, Ge SiC, SiGe AlP, AlAs, AlSb, GaP, GaAs, GaSb, InP, InAs, InSb ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe 4

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Composition General Material Properties Examine the general nature of semiconductor materials Conductivity : insulator  semiconductor  metal Composition Elemental semiconductor: group IV (Si, Ge) Compound semiconductor: group III & V (or II & VI) (GaAs, ZnSe, and alloys like AlxGa1-xAs Si : the most important of the semiconductors  major ICs including CPU GaAs : superior electron transport properties and special optical properties  laser diode, LED, and high speed ICs Binary : two elements Ternary : three elements

Purity Dopants can have a drastic effect on the electrical properties of semiconductors Typically, dopant atoms at levels ranging from one part per 108 to one impurity atom per 103 semiconductor atoms will be purposely added to the semiconductor to control its electrical properties Structure Amorphous Polycrystalline : grain, grain boundary Single crystal : electrical properties are superior

The Unit Cell Concept Crystal Structure Lattice = periodic arrangement of atoms in the crystal Lattice point = a dot which represents a particular atomic array Unit Cell = a small volume of the crystal that can be used to reproduce the entire crystal Primitive cell = the smallest unit cell that can be repeated to from the lattice

Simple 3-D Unit Cells simple cubic = sc, body-centered cubic = bcc, face-centered cubic = fcc lattice constant Pedantically현학적으로

Semiconductor Lattices The diamond structure For Si, 8 atoms in a cell a=5.43 Å (1 Å =10-8 cm) 8/a3=5.221022 cm-3 A unit cell of the diamond lattice constructed by placing atoms ¼, ¼, ¼ from each atom in an fcc; (b) top view (along any <100> direction) of an extended diamond lattice. The colored circles indicate one fcc sublattice and the black circles indicate the interpenetrating fcc.

Miller Indices Single crystal silicon wafers (6” and 8”) typical of the starting substrates

p=3, q=2, s=1  (236) plane Indexing procedure: Intercept set in the order x, y, z Invert the intercept values Convert the 1/intercept set to the smallest possible set of whole numbers Enclose the whole number set in curvilinear brackets p=3, q=2, s=1  (236) plane Miller indices

Horizontal Bridgman method Czochralski method Crystal Growth Horizontal Bridgman method Czochralski method                                                                                                  Czochralski method Fig. Pulling up of Si crystal from molten material. (a) Schematic of crystal growth process. (b) A view from an entrance of a furnace.                                                                                           Horizontal Bridgman method Fig. Crystal growth from a molten material in a crucible. (a) Solidifying from one side end of molten material (b) Melting and solidifying in an operation band 14